The invention relates to hoisting devices and, more particularly, to accessories and methods for hollow stem auger retraction from downhole in (eg., from down in the hole of) a well bore. The conventional occasion nowadays for wanting to withdraw a string of hollow stem auger sections from a well bore is during construction of an environmental monitoring well.
Briefly, groundwater monitoring/remediation wells are bored into the earth. A bore hole is formed by down-feeding a string of hollow stem auger sections. What is loosely referred to as an “auger” is actually more technically accurately referred to as a string—or end to end assembly—of numerous individual sections of hollow stem auger sections. FIGS. 7 and 8 (among others) shows the top end of one such section 21 (ie., a hollow stem auger section 21).
Briefly, FIGS. 7 and 8 show that the hollow stem auger section 21 has a hollow stem (naturally enough) that at the top end thereof is necked down to form a top collar 22. The remainder of the hollow stem auger section 21's hollow stems outer surface support a helical flight 23, which helical flight 23 typically has a pitch about equal to the outside diameter thereof. The top collar 22 is provided with features and adaptation to couple with a drill cap 24. That is, the top collar is formed with four angularly-spaced, vertical, external flutes 25 and two diametrically opposite pin holes 26. Correspondingly, the drill cap 24 has four angularly-spaced, vertical, external splines 27 and two diametrically opposite pins 28 (or bolts).
Now let's turn to the matter of boring a bore hole to its deepest depth. An auger string is progressively elongated by the addition of additional sections 21 in an end to end assembly thereof (this is not shown, and the bottom end of each section is formed with a bottom collar which has counterpart formations as the drill cap 24). This activity of progressively elongating the auger string takes place in alternating fashion with boring out the bore hole about the length of one such section 21. When the deepest depth is reached, the auger string is typically not just stopped at the deepest depth but retracted a foot or so (−30 cm). Then, the drill cap 24 is displaced off the topmost section 21 (eg., as shown in FIG. 7). A sand and/or grout footing is poured into the hollow center (lumen) of the hollow stem auger string. Then an undersized casing is inserted into the lumen of the hollow stem auger string all the way to where it bottoms out onto the recently poured in footing.
Typically the casing comprises an assembly of PVC pipe sections which are twisted together with counterpart internal and external threaded ends to form a sealed string of casing sections as a whole. However, the first section of the casing string comprises a screen section. The screen section is typically a ventilated stainless steel assembly to allow groundwater to seep in at the lowest ten feet (−3 m) or so of the monitoring/remediation well.
Again, the casing—typically a string or end-to-end assembly of PVC pipe sections twisted together by the counterpart internal and external threaded ends thereof—is undersized:—relative to, that is, the lumen of the hollow stem auger string in which it is inserted. Thereafter, the hollow stem auger string is withdrawn from the bore, leaving the PVC-pipe casing string in place. Thus such an undersized casing string presents an annular gap between the bored earth and PVC pipe sections. This annular gap is then backfilled. About the lowest ten feet (−3 m) or so surrounding the screen section is backfilled with sand, to allow seepage of groundwater. The remaining depth (dozens or hundreds of feet or meters) is backfilled with cement or the like, bentonite being a common substitute, to disallow the seepage of groundwater.
Well casings are specified among three or so standard sizes and according to pipe diameter. For example and without limitation, a remediation well might be specified to be cased with any of two-inch pipe, four-inch pipe, or six-inch pipe and so on (eg., about five, ten and fifteen cm O.D. respectively). If two-inch pipe is specified, then the lumen of the hollow stem auger string typically measures about 4¼ inches (−11 cm) inside diameter. The PVC pipe typically measures about 2⅓ inches (−6 cm) O.D. During withdrawal of the hollow stem auger string, an extension of the PVC pipe is left poking up out the top of lumen of the hollow stem auger string so that none of the footing back fill is errantly poured into the casing string's hollow core (and into the inside of the screen).
To turn to another matter of the prior art, there is another piece of the background to note, which involves the field equipment used by the workers in this industry:—eg., their drilling rigs. Namely, such drilling rigs have two kinds of devices for retracting the hollow stem auger string:—ie., one being hydraulically-winched cables or lines, in contrast to, the other being hydraulic cylinders.
It might be noted that hydraulically-winched cables and lines, when used to pull free a stuck object, typically include the danger of recoil. Conversely, hydraulic cylinders are essentially recoilless in the same situation. Also, the hydraulic-cylinder systems of such drilling rigs are powerful, and typically outmuscle the power of the hydraulic winches by several times.
A typical drilling rig utilized in the industry might comprise, for example and without limitation, a CME 750 All-terrain (rubber tire) vehicle drilling rig of the Central Mine Equipment Company in St. Louis, Mo. This is the carrier/drilling rig combination which is approximately illustrated in several patents of the CME Company, and for more particular disclosure of such carrier/drilling rig features, reference may be had to any of U.S. Pat. Nos. 3,527,309; 3,561,545 and/or 4,638,871—all of which are by C. L. Rassieur. The foregoing patent disclosures are incorporated fully herein by this reference thereto.
Such a carrier/drilling rig has a two-piece tower comprising, in the lower portion thereof, an undergirding upright, upon which is affixed a removable mast. The crown of the mast might be outfitted with as many as five sheaves. In a five sheave configuration, typically one sheave serves a wireline cable and winch, another serves softlines perhaps pulled by a cathead, and the remaining three would typically serve three cable-and-winch systems for winching up (eg.) sections of drill rod. The wireline cable and softline-cathead system are not pertinent to the present invention. Typically the wireline cable system reels up a wire relatively fast but with a weak hoist (eg., able to exert 900 pounds or −400 kg of force or so) and is utilized in rock-coring, for example. The cathead is like a capstan on a ship, except oriented on a horizontal turning axis, and can winch in by means of one or two loops of not only softlines but also cables and/or chains as well. It typically is a weak system too.
Stronger still are the (three or so) cable-and-winch systems. It is typical to equip the drilling rig with winches rated between about 1,800 or to 3,200 pounds (−700 to −1,400 kg). It is also known to include at least one cable-and-winch system as a main one for fishing stuck objects and the like, and provide it with a retraction-force rating as high 10,000 pounds (−4,500 kg). Again, these three cable-and-winch systems are designed for, among other end uses, lifting up sections of drill rod. The height of the tower to the crown of the mast is typically something greater than twenty feet (−6 m) since that is a standard length of sections of drill rod. The above-ground height of the sheaves for the CME 750 ATV is about twenty-seven and a-half feet (−8⅓ m), which means that workers can hoist the twenty-foot rods with clearance to spare. When the CME 750 ATV is equipped with three such hoists (ie., cable-and-winch systems), workers can pull sixty feet of rods without having to lay any down on the ground or on the deck.
The upright (again, which undergirds the detachable mast) comprises legs and a standing rotary drive shaft (eg., a kelly bar, sometimes a square bar). The standing rotary drive bar typically has a lower end anchored in a main rotary drive and an upper end held in a bearing. The legs carry between (or among) themselves a traveling rotary table. Drive input to the rotary drive table is received from the standing rotary drive shaft as the traveling rotary table transits up and down the standing rotary drive shaft. The drill drive is typically a pair of serially-suspended links interconnected by a U-joint.
The hydraulic vertical drive system for cycling the traveling rotary drive table between feed (eg., pulldown) and retraction strokes typically comprises hydraulic cylinders which serve double-duty as the legs for the upright. The main rotary drive and the hydraulic vertical drive system are typically the strongest systems on the carrier/drilling rig. That is, the main rotary drive might deliver 10,000 ft-lbs (−13,5000 Nm) of rotary torque. The hydraulic vertical drive system can typically deliver a feed (pulldown) force in excess of the weight of the vehicle, or something on the order of 20,000 pounds (−9,000 kg).
The outstanding feature of the hydraulic vertical drive system is the retraction force it can develop:—30,000 pounds (−13,600 kg) for the CME 750 ATV, and then 40,000 pounds (−18,000 kg) being no problem for other models. As an aside, another aspect of the hydraulic vertical drive system is that its drive stroke is only about five and a-half feet (−1⅓ m), but which works out to be sufficient for clearance of sections of hollow stem augers, since they conventionally are a standard five feet (−1½ m) in length.
More importantly, the hydraulic vertical drive system has no cables which can stretch (nor chains which need lubrication). Better yet, the hydraulic vertical drive system is substantially recoilless. When feeding down or retracting up against a stuck hollow stem auger string, as soon as the sticking force is overcome the hydraulic vertical drive system does not recoil. In contrast, cables stretch or the stuck hollow stem auger string (if being retracted up) can let fly after being unstuck (or after being torn apart), chains can whip and so on. Moreover, cables can snap, so can chains. Accordingly, the hydraulic vertical drive system gives precise control over the force applied to downhole tools or objects.
Arguably most significant of all is that, its brute power aside and in spite of being the most powerful system on the carrier/drill rig, the hydraulic vertical drive system is probably the safest.
Now let's return the discussion back to the present problem. Hollow stem auger sections 21 interconnect with each other by their top and bottom collars (only a top collar 22 is shown in FIGS. 7 and 8). The topmost hollow stem auger section 21 is down fed into the bore hole by the drill cap 24 attached to the drill drive (not shown, or extension thereof, also not shown) of the drill rig (not shown). FIGS. 7 and 8 shows a drill cap 24 and the top collar 22 of the hollow stem auger section 21. As previously described, the top collar 22 has four angularly-spaced, vertical, external flutes 25 and two diametrically opposite pin holes 26. Correspondingly, the drill cap 24 has four angularly-spaced, vertical, external splines 27 and two diametrically opposite pins 28 (or bolts). By such formations and/or adaptations, the drill cap 24 and top collar 22 couple as shown in FIG. 8.
During the withdrawal of the hollow stem auger string, an extension of the PVC pipe is typically poking up out the lumen of the hollow stem auger string. Hence the drill cap 24 cannot be coupled to the top collar 22 of topmost hollow stem auger section 21 of the hollow stem auger string. The reasons include either because sand, mud or grout has caked and fouled the top collar 22's flutes 25, or else because the poking up PVC pipe is in the way.
Again, when constructing a well, workers usually have made a mess (understandably so, since it is a messy process in an environment of messy materials) on the top collar 22 of the topmost section 21 of the hollow stem auger string. Hence they cannot reliably get the drill cap 24 to couple. Sometimes, the PVC casing pipe floats up a little bit which adds to the height of the poking up part. So to date workers in this industry have been predominantly relying on a single hook device of the prior art.
To be more particular, since this is important to understanding the shortcomings of the prior art, such prior art hollow stem auger hoists typically comprise a single hook construction. That is, prior art hollow stem auger hoists have just one hook to insert in one or the other of the two diametrically opposed pin holes 26 in the top collar 22 of the topmost section 21 of the hollow stem auger string. Shortcomings with the prior art single hook include (1) it pulls the hollow stem auger string from an axis that is offset from the central axis of the string, (2) and this in consequence tends to bind the single hook in the hole 26, either sometimes deforming the hole 26 in consequence, and/or during other times, making it difficult for a worker to manually pull the hook out of the hole 26, and (3) when winching the bare hook up on a cable around the work site and equipment thereof, the bare hook frequently catches an unintended piece of equipment, such as and without limitation any part of the two-piece tower, either the undergirding upright or the affixed a removable mast. Hence the hook can catch and damage a piece of equipment or such structure/superstructure thereof.
Nevertheless, drillers have been accustomed to the single hook method of withdrawing the hollow stem auger string, and then continuing to use the hook to support the topmost hollow stem auger section 21 as it is disengaged from the string and set aside (eg., as on the ground, or on storage racks).
What is needed is a solution to overcome the shortcomings of the prior art.
A number of additional features and objects will be apparent in connection with the following discussion of the preferred embodiments and examples with reference to the drawings.